(a) Field of the Invention
The present invention relates to a transmit power control method of a terminal in direct communication between terminals, and a terminal supporting the same.
(b) Description of the Related Art
Recently, in order to implement social networking between neighboring users, public safety, and the like, device to device (D2D) communication in which communication is directly performed between terminals without going through a base station has been discussed in the 3GPP Standards Association, and the like.
In typical cellular communication, the terminal controls interference between surrounding cells by adjusting transmit power. Particularly, transmit power of a reverse (uplink) terminal is set as expressed in the following Equation 1 depending on a distance from the base station, a modulation and coding scheme (MCS) level, and the like.
                              P          UE                =                  min          [                                    P              MAX                        ,                                                                                                      P                      0                                        -                                          α                      ·                      G                                                        ︸                                                  OL                  ⁢                                                                          ⁢                  operating                  ⁢                                                                          ⁢                  point                                            +                                                                                          Δ                      TF                                        +                                          f                      ⁡                                              (                                                  Δ                          TPC                                                )                                                                              ︸                                                  dynamic                  ⁢                                                                          ⁢                  offset                                            +                                                                                          10                      ·                                              log                        10                                                              ⁢                    M                                    ︸                                                  BW                  ⁢                                                                          ⁢                  factor                                                              ]                                    [                  Equation          ⁢                                          ⁢          1                ]            
In Equation 1, G represents path loss between the terminal and the base station, and an open loop (OL) operating point represents compensation for the path loss. A dynamic offset represents adjustment of the transmit power taking account of the modulation and coding scheme (MCS) and transmit power control (TPC) of a network which are used. In addition, a bandwidth (BW) factor is a parameter taking account of the number of assigned resource blocks (RBs).
The OL operating point is the most important factor when the terminal sets the transmit power based on Equation 1. In the OL operating point, P0 is a base value which is used to control a signal-to-noise ratio (SNR) target value, and may be set as expressed in the following Equation 2.P0=α·(γtgt+PIN)+(1−α)·(PMAX−10·log10M)  [Equation 2]
In Equation 2, α represents a path loss compensation parameter and PIN represents expected values for noise and interference amount. γtgt refers to a target signal-to-noise ratio (SNR). α=0 refers to a fixed P0 and α=1 refers to complete compensation for the path loss. In general, α is set to a range of 0<α<1, and as a result, a reverse transmit power method of a terminal in a cellular communication system is called fractional power control (FPC).
The D2D communication does not use a different frequency than that of the cellular communication system, but reuses the same frequency. As such, since the frequency of the cellular communication system is reused in the D2D communication, service capacity that a user actually experiences may be improved. In this case, the transmit power of the terminal which has performed the D2D communication has an important effect on the entire system performance as well as performance of a D2D link itself due to an effect of interference between D2D links and mutual interference with a cellular link. Therefore, there is also a need to control transmit power of the terminal performing the D2D communication.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.